Fix comment_create verification

## Why
Lost in a rebase. The GUI clamping was just meant to complement this (so that user knows what's going on), but ended up being the only thing that was pushed.

## Changes
- If the fetch failed or still in progress, we ask the user to wait or simply refresh the page.
- If already commented from another channel, bail and inform via Toast.

static/app-strings.json

@@ -2257,6 +2257,9 @@
   "Attach images by pasting or drag-and-drop.": "Attach images by pasting or drag-and-drop.",
   "There was a network error, but the publish may have been completed. Wait a few minutes, then check your Uploads or Wallet page to confirm.": "There was a network error, but the publish may have been completed. Wait a few minutes, then check your Uploads or Wallet page to confirm.",
   "Already reacted to this comment from another channel.": "Already reacted to this comment from another channel.",
+  "Commenting from multiple channels is not allowed.": "Commenting from multiple channels is not allowed.",
+  "Failed to perform action.": "Failed to perform action.",
+  "Please wait a while before re-submitting, or try refreshing the page.": "Please wait a while before re-submitting, or try refreshing the page.",
   "Unable to react. Please try again later.": "Unable to react. Please try again later.",
   "Username (cannot be changed)": "Username (cannot be changed)",
   "Display Name": "Display Name",

ui/redux/actions/comments.js

@@ -16,6 +16,7 @@ import {
   selectPendingCommentReacts,
   selectModerationBlockList,
   selectModerationDelegatorsById,
+  selectMyCommentedChannelIdsForId,
 } from 'redux/selectors/comments';
 import { makeSelectNotificationForCommentId } from 'redux/selectors/notifications';
 import { selectActiveChannelClaim } from 'redux/selectors/app';
@@ -620,6 +621,7 @@ export function doCommentCreate(uri: string, livestream: boolean, params: Commen
 
     const state = getState();
     const activeChannelClaim = selectActiveChannelClaim(state);
+    const myCommentedChannelIds = selectMyCommentedChannelIdsForId(state, claim_id);
     const mentionedChannels: Array<MentionedChannel> = [];
 
     if (!activeChannelClaim) {
@@ -627,6 +629,23 @@ export function doCommentCreate(uri: string, livestream: boolean, params: Commen
       return;
     }
 
+    if (myCommentedChannelIds === undefined) {
+      dispatchToast(
+        dispatch,
+        __('Failed to perform action.'),
+        __('Please wait a while before re-submitting, or try refreshing the page.'),
+        'long'
+      );
+      return;
+    }
+
+    if (myCommentedChannelIds && myCommentedChannelIds.length) {
+      if (!myCommentedChannelIds.includes(activeChannelClaim.claim_id)) {
+        dispatchToast(dispatch, __('Commenting from multiple channels is not allowed.'));
+        return;
+      }
+    }
+
     // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll
     // $FlowFixMe
     const mentionMatches = [...comment.matchAll(MENTION_REGEX)];

ui/redux/selectors/comments.js

@@ -478,7 +478,7 @@ export const selectChannelMentionData = createCachedSelector(
  *
  * @param state
  * @param claimId
- * @returns {null | undefined | Array<string>} 'undefined' = "not fetched"; 'null' = "no claim";
+ * @returns {null | undefined | Array<string>} 'undefined' = "not fetched for this ID"; 'null' = "no claim";
  */
 export const selectMyCommentedChannelIdsForId = (state: State, claimId: string) => {
   return claimId ? selectState(state).myCommentedChannelIdsById[claimId] : null;